Gain, AGC and overload

Three controls, three jobs

RF gainGain×Gain describes the ratio of output to input level. In a receiver it can occur before or after digitisation and is often expressed in dB.Example & full explanation → changes level inside the receiving chain. Volume instead determines how loudly already demodulated audio is played. AGCAGC×Automatic Gain Control adjusts gain according to signal level, reducing differences between weak and strong signals at the output.Example & full explanation → automatically adjusts gain to manage large level changes. Exactly where it acts depends on the receiver architecture.

If extra gain makes both signal and noise equally louder, the signal-to-noise ratio does not improve. Too little gain before digitisation can, however, use the converter’s available range poorly. The appropriate setting is therefore a compromise that considers all signals present.

A strong neighbour can limit reception

A strong transmitter outside the channel you are listening to can overload an early amplifier or the ADC. Possible symptoms include apparent extra signals, distorted audio or a raised noise background. A narrow software filter after the overloaded stage cannot undo distortion already created.

Compare with reduced RF gain or a suitable attenuator ahead of the receiver. If unwanted products decrease disproportionately and the wanted signal becomes clearer, overload is a plausible cause. This is a clue rather than a complete measurement; the antenna, preselection and local interference also deserve investigation.

Compare AGC deliberately

Fast AGC responds quickly to strong impulses but can audibly pump. A slower setting often keeps speech steadier, yet recovers later from strong signals. Compare with unchanged filtering and similar volume. On a shared web receiver, some hardware controls may affect all users or may not be accessible at all.

Equipment from my station

Find the corresponding equipment information here. The learning examples above are general explanations, not measurements of these devices.